[plug] ext4 fragmentation

Alastair Irvine alastair at plug.org.au
Sun Jun 18 00:05:32 AWST 2017

On Fri, 17 March, 2017 at 01:06:47PM +0800, Brad Campbell wrote:
> G'day all,
> I'm approaching my 6 yearly HD replacement on my bulk storage array.
> Current array is 14 x 2TB drives in a RAID6 with an ext4 filesystem.
> This array was re-built with a fresh format in 2013, so it has about
> 4 years heavy use on the filesystem.
> Having said that, the 1TB file copied across to the replacement
> array was giving me ~900MB/s until I used e4defrag on it. Now it's
> down to 500MB/s. So things are not perfect in defrag land.

Hmm... seems like there might be a mismatch between your filesystem
block size and your RAID chunk size.  Or something.
Anyone who's deal with RAID at a more detailed level than I have may be
able to expand on this.

Are you using software or hardware RAID?

*engages off-topic mode*
*puts on fogey hat*

This reminds me of using the Norton Disk Doctor to defrag FAT32
filesystems under MS-DOS.  And then when DOS 6 came out it had its own
defrag tool!  You can smell the nostalgia.

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